Field of the Invention
The present invention relates to lithography systems, particularly to removing hydrocarbon contamination emanating from a resist coated wafer under radiation exposure, and more particularly to an apparatus and method for cleaning resist outgassing windows.
In lithography systems involving radiation (photons, electrons) of resist coated wafers, resist outgassing would contaminate lithographic optical components with highly absorbing carbonaceous material, unless such contamination is intercepted. One means for physically intercepting hydrocarbon contamination emanating from a resist coated wafer under radiation exposure is to provide a resist outgassing window which is capable of transmitting the lithographic radiation while physically intercepting the hydrocarbon contamination. The problem associated with the use of resist outgassing windows is that as hydrocarbon contamination from resist outgassing builds up on the window, the window's transmission becomes degraded, eventually to an unacceptable level. This resist-outgassing problem will become more acute with the next generation lithography systems, such as the extreme ultraviolet (EUV), Scattering with Anguler Limitation Projection Electron Lithography (SCALPEL), and the 193 nm lithography systems. Thus, there is a need in the art for an effective means to clean the contamination from the window without physically removing the window from the lithographic tool. An ideal method would continuously clean the window during lithographic operation. A less ideal, but still desirable, method would permit in-situ cleaning of the window in a maintenance period (not during lithographic operation) without removal of the window.
The present invention is directed to a solution of the hydrocarbon contamination problem, and involves an apparatus and method which enables in-situ cleaning of resist outgassing windows during lithographic operation or during a maintenance period without removing the window. The present invention permits removal of hydrocarbon contamination from resist outgassing windows in a highly flexible manner, and is compatible with windows made of any material.